Charles martin clark



(No Model.)

0. M. CLARK. BURGLAR ALARM.

No. 541,719. Patented June 25, 1895.

WITNESSES. /NVENTOF? A TTOfiNE 78.

UNITED STATES PATENT OFFICE.

CHARLES MARTIN CLARK, OF NEIV YORK, N. Y.

BURGLAR--ALARM.

SPECIFICATION forming part of Letters Patent No. 541,719, dated June 25, 1895.

Application filed A ril 12, 1895, Serial No, 545,492. (No model.)

To all whom it may concern.-

Be it known that 1, CHARLES MARTIN CLARK, of New York city, in the county and State of New York, have invented a new and Improved Burglar-Alarm, of which the follow ing is a full, clear, and exact description.

The object of the invention is to provide a new and improved burglar alarm which is simple and durable in construction, very effective in operation, and arranged to instantly sound an alarm whenever an unauthorized person enters or moves about in a building.

The invention consists principally of an electric circuit, containing a magnetic coil to influence the electric current, by a person moving toward or from the said coil, a galvanometer arranged in the said circuit, and an alarm controlled by the said galvanometer.

The invention also consists of certain parts and details and combinations of the same, as will be fully described hereinafter and then pointed out in the claims.

Reference is to be had to the accompanying drawing, forming a part of this specification, in which the figure is a side elevation of the improvement, with part in section.

The improved burglar alarm is provided with an electric circuit A, supplied with elec tricity from a battery B or other suitable means. In the wires of the circuit A is arranged one or more magnetic coils C, located in the building to be protected, either under the floors, in desks, ceilings or other fixtures in the building. In the circuit A is also arranged a galvanometer E, normally standing at a zero position, but when one of the coils O is influenced by a person coming near the said coil, or walking away therefrom, then the needle of the galvanometer is deflected in the corresponding direction, to close an electric circuit F containing an alarm G.

The primary circuit A is provided with a suitable switch II, and a like switch I is arranged in the circuit F,so that both the alarm G and the circuit A may be shunted whenever desired, but usually during the day, when the burglar alarm is not needed. The galvanometer shown in the drawing represents the usual DArsonval galvanometer, but it is evident that a galvanometer of any approved construction may be used.

The contact of the needle is made with drops of mercury connected with the wires for the circuit F. It is understood that a person moving toward one of the coils 0, changes the activity thereof, so as to cause a deflection of the needle of the galvanometer E in one direction, to close the circuit for the circuit F and sound the alarm G. In a like manner when a person moves away from the coil, the activity of the same is again changed and a deflection of the needle of the galvanometer in an opposite direction takes place, and again the contact is made, to close the electric circuit F and to again sound the alarm G.

It is understood that the alarm and galvanometer may be placed in a central station outside of a building, or in the janitors or Watchmans room within the building, so that whenever an unauthorized person enters or moves about in the building, the alarm is sounded to bring the proper oiiicials to the spot.

It will further be seen that if the wires of the circuits are cut or shunted, a deflection of the needle of the galvanometer takes place, so that the circuit is closed and the alarm G is sounded. It is further understood that it does not make any difference if the building is built of metal or a non-conducting material, as the galvanometer is so set as to assume a zero position after the several parts are in place, the necessary resistance being placed in the circuit.

Any tampering with the wires in the circuit A will be instantly discovered upon setting the alarm, as only a substitute of equal resistance would cause the galvanonieter needle to come to a rest at the point, the resistance of the coil 0 being only known to responsible persons.

A suitable aluminum wire in mercury contacts the balance between two mercury cups on the top of the galvanometer, as indicated in the drawing.

It is further understood that any stationary iron in the magnetic field will not produce a deflection, but whenever a person having metal upon his body moves into the magnetic field or away therefrom, the galvanometer is actuated. 0n the other hand, a piece of soft iron may be suspended or arranged near the coil, so that when a person not having any iron on his body approaches or moves from the magnetic field, then the jarring of the floor or other part of the structure causes the soft iron to vibrate and disturb the magnetic field of the coil, and consequently cause a deflection of the galvanometer.

By the arrangement described, it is not necessary in order to ring the alarm that a door, window or other device he opened or closed, as the alarm is sounded by a person entering and moving about in the building.

Having thus fully described my invention, I claim as new and desire to secure by Letters Patent 1. A burglar alarm, comprising an electric circuit, one or more magnetic coils, a galvanometer in the said circuit and actuated by a person moving and causing the movement of a metal into or out of the magnetic field of circuit containing one or more magnetic coils,.

a galvanometer in the said circuit and having its needle normally standing at zero, and

a second electric circuit containing an alarm, and adapted to be closed by the action of the said galvanometer whenever a person causes the movement or vibration of a metal in or out of the field of one of the said coils, substantially as shown and described.

vCHARLES MARTIN CLARK. Witnesses: 'IHEo. .G. HOSTER, O. SEDGWICK, 

